This invention relates generally to hydraulic systems for internal combustion engines. More particularly, this invention relates to hydraulic stems having a combination filter screen and gasket to remove debris from the hydraulic fluid in a fuel injection system with a high-pressure pump and a priming reservoir.
In engine manufacturing, metal chips and other debris may remain in the engine even when engine parts are cleaned prior to assembly. By their nature, fittings with tapered thread connections create metal chips when assembled into a threaded hole. Machining also may leave metal chips. Casting processes may leave other debris in core passages and crevices. As a result, engines inevitably have some debris inside deep-drilled holes, cast-in core passages, and other places. During engine operation, the heating and cooling of the engine releases this debris into the hydraulic fluid. As the hydraulic fluid flows, the metal chips and other debris move throughout the hydraulic system.
The metal chips and other debris may interfere with proper operation of the engine. This interference is more problematic for engines with hydraulically actuated fuel injection systems. In these engines, a priming reservoir typically is disposed at a level higher than the inlet to the high-pressure pump. The priming reservoir includes a lower reservoir portion usually cast into the engine front cover. An upper reservoir portion is attached to the lower reservoir portion to increase the reservoir volume. A gasket seals the lower and upper reservoir portions. The priming reservoir provides gravity feed to the pump during engine start-up. Any debris in the hydraulic fluid tends to accumulate in the priming reservoir. On engine start-up, the pump drives accumulated debris throughout the hydraulic system. While the engine is running the pump continues to drive debris through the hydraulic system.
Debris in the hydraulic fluid may obstruct sensors, valves, and other parts of the hydraulic system and, especially, the hydraulic-actuating portion of the fuel injector system. Metal chips may clog injector pressure regulators, high-pressure pumps, injectors, and pressure control valves because these parts typically are manufactured to very close tolerances. Even though some parts (e.g., the pressure control valve) have internal filters (e.g., an edge filter), too much debris may clog and prevent proper function of these filters.
Accordingly, there is a need for a filter screen to remove debris from the hydraulic fluid of an internal combustion engine, especially those with hydraulically actuated fuel injection.
The present invention provides a hydraulic system with a filter screen for removing debris from hydraulic fluid in an internal combustion engine. The filter screen is disposed between the upper and lower reservoir portions which form a priming reservoir for the hydraulic system. In the engine, an upper reservoir structure may be mounted on a front cover at an interface. The front cover forms the lower reservoir and has a top edge with a depression. The upper reservoir structure forms the upper reservoir and has a bottom edge. The top and bottom edges form the interface.
The filter screen is located at the interface and may have a gasket and a screen assembly. The gasket is located along the interface inside the depression for sealing the upper reservoir structure to the front cover. The depression""s depth and the gasket""s thickness control the xe2x80x9csqueezexe2x80x9d on the gasket.
The screen assembly has a plate member located at the interface for connecting with the gasket. The plate member forms an aperture having a cross-section area. A filter screen is connected to the plate member for enclosing the aperture.
In one embodiment, the plate member is integrally connected to the gasket. The plate member has bonding holes along its periphery. When the gasket is formed on the plate member, the gasket material fills the bonding holes to mechanically connect the gasket to the plate member. The edges of the plate member may be treated with a bonding agent to chemically bond the gasket to the plate member.
In another embodiment, the plate member is not integrally connected to the gasket. The loose gasket is placed in the depression at the top edge of the front cover. The plate member is positioned inside the gasket and between the upper reservoir structure and the front cover. The plate member is thinner than the depth of the depression, but extends to contact the gasket along its periphery. Once assembled, the gasket deforms to create a face seal between the upper reservoir structure and the front cover. The gasket also seals around the edges of the plate member.
In either embodiment, the filter screen separates the upper and lower reservoirs, forcing the hydraulic fluid to pass through the filter screen. The filter screen retains any debris in the hydraulic fluid larger than the filter screen""s mesh size.
The filter screen has an open area large enough to provide the desired pressure drop for operation of the pump. Consequently, the filter screen may have a surface area larger than the cross-section area of the aperture. If so, the filter screen has an open end and a closed end. As shown, the filter screen has a cylindrical shape. However, it may have other shapes including conic, rectangular, or flat. In addition, the filter screen has a mesh size to retain particles large enough to cause damage to the hydraulic system or other parts. The screen assembly may have a flange for connecting the filter screen to the plate member. A flange would facilitate producing a solid weld for joining the filter screen to the plate member.
In another embodiment, the plate member may have a basket assembly. The basket assembly mechanically supports and may be connected to the filter screen. The basket assembly, the plate member, and the filter screen may be a single part. While the screen assembly may be made from other materials and combinations of materials, the basket assembly is preferred when the screen assembly is made of plastic.
The following drawings and description set forth additional advantages and benefits of the invention. More advantages and benefits are obvious from the description and may be learned by practice of the invention.